1. Technical Field
The present invention is directed toward window sash locks, and more particularly toward pick resistant check rail sash locks for double hung windows.
2. Background Art
A check rail lock draws together meeting rails of an upper and lower sash of a double-hung window and locks the sashes against opening movement. The check rail lock has a housing which mounts a rotatable cam for movement between locked and unlocked positions and which engages a keeper in a locked position. The cam is limited to movement between the locked and unlocked positions.
Some prior art cam locks (e.g., U.S. Pat. Nos. 4,736,972 and 5,110,165) have included spring structures which releasably bias the cam toward, and retain the cam in, locked and/or unlocked positions. Such locks provide increased security, although it may still be possible for a skilled person to cause such check rail locks to open. Specifically, skilled intruders may be able to manipulate the structure with a knife or stiff wire introduced from outside the window which is capable of overcoming the biasing force of the spring structure, thereby gaining silent access to a dwelling through the double-hung window. (It should be recognized that although such locks are often used on glass windows which could be easily broken to allow the intruder to reach in and open the lock, doing so can be noisy and attract the attention of people both inside and outside the dwelling, and that risk of attention can significantly deter potential intruders who are unable to otherwise gain access by silently manipulating the lock). Still other cam locks (e.g., U.S. Pat. No. 5,219,193) have provided a mechanism for locking the handle and cam in the locked position in order to keep an intruder from opening the lock from the outside. Such locks provide enhanced security but can also make the lock more difficult to normally operate by persons inside the dwelling. For example, where a push button is used to secure the lock in position, an operator will have to do two steps to open the lock (push the button, and then turn the cam). Such operation might not be readily understood by some people, and can potentially be difficult for persons of limited mobility (e.g., with arthritis).
The present invention is directed toward overcoming one or more of the problems set forth above.